1. Field of the Invention
The present invention relates to an integrated circuit (IC) socket used for mounting an IC package such as a central processing unit (CPU) or a large scale integrated circuit (LSI) onto a printed circuit. More specifically, the present invention relates to an IC socket including a three-dimensional circuit formed by use of a three-dimensional circuit forming technique, and to a manufacturing method thereof.
2. Description of the Related Art
Techniques for mounting an IC package such as a central processing unit (CPU) or a large scale integrated circuit (LSI) onto a printed circuit with a socket have long been studied. IC sockets for mounting CPUs in land grid array (LGA) packages or ball grid array (BGA) packages are embedded in many personal computers and mother boards of servers.
To improve functions and performances of CPUs, the number of pins and the processing speed have been increasing. With the increase in the number of pins and the processing speed of CPUs, IC packages have been improved to have a larger size and finer pitch and IC sockets have been also improved similarly, in order to support such CPUs having an increased number of pins. The increase in size of an IC package for supporting the increased number of pins increases the flexible volume of the IC package and variations in the height of contact lands and balls thereof.
Accordingly, an IC socket also needs to correspond to these increases, and is required to have a structure capable of securing contact strokes of the IC socket. Meanwhile, support for the finer pitch should be achieved with the simplest structure possible, and a desirable structure is one in which an IC package is connected to a printed circuit board at a short distance. Moreover, for the increase in the speed of a CPU, it is important that a contact between the IC socket and the package has low inductance. Here, it is also expected to achieve a high allowable current in response to an increase in a consumption current attributable to the higher speed.
The mainstream of a socket for a LGA package today is one corresponding to 400 to 800 pins at a pitch of about 1 mm with a structure in which given shapes of contacts are formed by intricately bending a metal plate, so that the contacts are inserted into a housing of the IC socket. However, these IC sockets are assembled by inserting the contacts one by one into the socket housings. Therefore, contact inserting time required for manufacturing is increased along with the increase in the number of pins and productivity is therefore deteriorated.
As a countermeasure for such a problem, there is known a structure using columns made of conductive elastomer as the contacts. However, the elastomer used as the contacts has higher contact resistance than metal contacts, which may increase a risk of heat generation or a voltage drop when a high current is applied to the contacts. Moreover, in the IC socket using the elastomer, the contacts made of the elastomer do not wipe (scrape) metal surfaces of lands (electrodes) on the IC package when an IC package is attached to the IC socket. For this reason, even if foreign materials bonds on the metal surfaces and the metal surfaces changes in quality by forming oxide films on the metal surfaces, removing foreign materials and oxide films on the lands is not expected. Moreover, the contact resistance of the IC socket may be changed over time, because this IC socket is in contact with the metallic lands on the IC package by means of pressure contact of the elastomer.